Q. 8. Which of the following statements about plastics are true? (i) All plastics do not have the same arrangement of monomer units.
(ii) Melamine resists fire and can tolerate heat better than other plastics.
(iii) Plastics with cross-linked monomers are also known.
(iv) Plastics have limited applications.

a) (i) and (iii) only
b) (iii) and (iv) only
c) (i), (ii) and (iii) only.
d) (i), (iii) and (iv) only

a) (I) and (iii) only

Explanation:

Because different plastics have different size.

(b) which contains higher levels of vitamin b, oranges or spinach?

explanation:

you can eliminate a, c, and d because they are questions based on opinions.

answer : third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol

explanation :

let us write down the given equations

equation 1 :

equation 2 :

equation 3 :

let us use hess's law to find out which 2 equations can be added to get the third equation.

let us reverse equation 2 and multiply it by 2. the new equation that we get is,

equation 4 :

let us add equation 1 & 4

the above equation is similar to equation 3 but has different value for dhrxn.

therefore third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol